A mother who killed her disabled daughter and then herself after suffering years of harassment from local youths was partly driven to do so because the police did not heed her pleas for help, an inquest jury found today.

The jury at the inquest of Fiona Pilkington, 38, and her 18-year-old daughter, Francecca Hardwick, also criticised a failure to share information between the police and the local council as one of the reasons why they did not respond to the calls for help.

This evening, the jury found that Francecca Hardwick was unlawfully killed by her mother who went on to kill herself.

The Independent Police Complaints Commission tonight said it was launching an investigation into the way the "distressing" case was handled, in particular, how seriously the police responded to Pilkington's calls for help.

The inquest at Loughborough town hall heard that Pilkington, her daughter and her son, Anthony Hardwick, who had severe dyslexia, endured more than 10 years of abuse from a gang of teenagers living on their street.

Pilkington's blue Austin Maestro was found ablaze on a layby by the side of the A47 near the family's home in Barwell, near Hinckley, Leicestershire, late on the night of 23 October 2007. On the front seats, firefighters found the severely burned bodies of Pilkington and Francecca. The rear seat had seemingly been set ablaze with petrol.

The jury found that Pilkington killed herself and her daughter "due to the stress and anxiety regarding her daughter's future, and ongoing antisocial behaviour".

It was then asked to report on whether the response of police and two councils contributed to the deaths of the pair.

To the question of whether the police properly responded to the 33 calls made by Pilkington over 10 years about antisocial behaviour, the foreman said the police's failure had an impact on Pilkington's decision to unlawfully kill her daughter and commit suicide.

He added: "Calls were not linked or prioritised."

Asked whether Hinckley and Bosworth borough council's response to complaints of antisocial behaviour contributed to the deaths, the foreman added: "Prior to February 2007, actions to control antisocial behaviour were not evident."

The jury also found that Leicestershire county council failed to properly help the family.

The foreman said: "A referral was not made for a professional assessment of Fiona's state of mind."

The jury had heard days of evidence chronicling the desperate attempts of a depressed, timid single mother with borderline learning difficulties to attract the sustained attention of officialdom to her plight before her death.

As well as the difficulties of coping with two extremely vulnerable children – Francecca had severe learning difficulties and needed constant care while her brother, Anthony, now 19, has serious dyslexia and attended a special school – Pilkington spent more than a decade "under siege" in her own home from local youths, the inquest heard.

Their 1930s semi-detached house was pelted with stones, gangs smashed bottles outside and jumped into the front hedge. On some weekend nights youths hung outside the house for hours on end, shouting taunts and insults.

In a harassment diary kept by Pilkington for a brief period in the year of her death she recounted shouts outside her living room window from 11.30pm until the early hours. The entry ends: "Sat in the dark until 2.30am, stressed out." The harassment would hit peak around Hallowe'en and Bonfire Night when flour, eggs and fireworks were aimed at the house.

The youths would imitate Francecca's walk and signal to her bedroom window for her to lift up her nightdress. Anthony was also targeted. On one occasion he was forced into a shed at knifepoint and locked inside, having to smash a window to escape, the inquest was told.

Apart from contacting police no fewer than 33 times – including 13 in the year of her death – Pilkington discussed matters with two antisocial behaviour officers from her borough council, dealt with a series of social workers and even wrote to her MP.

But not one person was convicted of a single crime, or even arrested, although the identities of the main culprits were known to both police and council officials. The council twice gave Pilkington diaries to chronicle the abuse, but neither was collected.

The inquest was also left with an increasing impression of organisational haphazardness – even chaos – with different agencies meeting regularly but failing to share information or even establish the basic facts of the case.

Although much of the abuse centred taunts at the children's disabilities, police failed to recognise it as a hate crime rather than simple antisocial behaviour, which would have made it a far higher priority.

The inquest heard that Leicestershire police had at the time of Pilkington's death not implemented Home Office guidance on hate crimes, issued two years beforehand.

Hinckley and Bosworth council's community officers visited Pilkington but never even learned until after she was dead that any member of the family was disabled.

An official who dealt with her case in 2004 moved to Australia and his successor did not learn of the family's problems for three years. Case files went missing or were destroyed.

The coroner, Olivia Davison showed signs of apparent bafflement that the family's desperate situation remained unrecognised by so many people who could have helped.

Questioning a senior social services manager from the county council, at one point she remarked: "If somebody had just sat this woman down with a cup of tea they could have perhaps helped her."

She also showed surprise at the lack of police action, noting that there were "seven or eight acts of parliament" under which the culprits could have been punished.

Davison said she planned to write a report to the head of Hinckley and Bosworth council, copied to the Ministry of Justice, following the inquest.

She said: "I am concerned about the evidence I have received in this inquest about the process for gathering and recording information from victims of antisocial abuse.

"The council representatives have given evidence of the manner in which information was collected from Fiona Pilkington, the forms completed, and the manner in which paperwork was dealt with.

"I am concerned about the process and my report will address the process.

At a press conference following the verdict, Leicestershire police apologised to the family for what went wrong and said it had instituted a series of changes, including training for officers to better recognise vulnerability.

The force's temporary chief constable, Chris Eyre, said he wanted to offer "an unreserved apology to the family, the community and the wider public".

He said: "We are extremely sorry that our actions failed to meet the family's needs. There are things in retrospect we would have done differently."

The findings of a serious case review by Leicestershire county council, also issued after the verdict, made a series of recommendations, including better communication between different agencies and more recognition of hate crimes against the disabled.

Speaking after the inquest on behalf of their family, Pam and David Cassell, Fiona's parents and Francecca's grandparents said:

"It's been almost two years since we tragically lost Fiona and Frankie and we still find it hard to take in. We miss them very much and think of them everyday.

"We are hoping that now the inquest is over we can try and get back to some kind of normality although our lives will never be the same again. This has been a terrible time for us and we wouldn't have managed without the love and support from our friends and family.

"This case has highlighted the difficulties that families with disabled children face. We know that the agencies involved have looked to see how they can improve the way they work. If this helps just one family then their deaths would not have been in vain and something good will have come out of this tragedy.

"We would also like to thank the coroner, Miss Olivia Davison, and those who have taken part in the inquest for being so thorough. Their efforts are very much appreciated."

The home secretary, Alan Johnson, called the case "shocking" and said police and councils had "some hard lessons to learn about past failures, which will be the subject of further investigations".

Responding to the verdict, the Conservative shadow home secretary, Chris Grayling, said: "This case has horrified the nation, and the police claim that they aren't responsible for tackling antisocial behaviour was completely shocking.

"We need real action to stamp out antisocial behaviour, to get more police out of police stations and onto the streets, and to demonstrate to law-abiding citizens that the criminal justice system really is on their side."